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wrapping headers

Joined
15 September 2004
Messages
737
Location
sacramento california
Hello. need advice.
1992 NSX. has comptech headers. always trouble getting it to smog california.
this time NOX high. shop says cats not hot enough.
shop suggests wrapping headers (which will keep gas hotter and therefore get cats to work)
my internet search on wrapping headers suggest wrapping headers can destroy the headers.
shop suggests also consider ceramic coating (which will be 1400 dollars).
what do you all think? the cats are 4 years old, after market.
Thank you.

1992 NSX comptech headers, koni shocks, later style rims, slammed
2008 tundra
2005 X3
 
My gut feel is that your 4yr old after market cats are the culprit. If I was in your shoes, i'd buy a used set of OEM cats instead of spending money on coatings or wrapping which might just be a bandaid. There seems to be some for sale in the marketplace here. While getting the cats up to operating temp is a common issue and is the default reason many smog shops use... most aftermarket cats are simply not as good as OEM or very high quality high flow cats like HJS.

With that said, I ceramic coated my Comptech headers inside and out. The place that did the work is Embee here in SoCal. I've driven this car at the track in all sorts of weather and with a supercharger. I've given them a beating and the coating is still in EXCELLENT shape with good thermal protection. The other place is called Swaintech in the east coast. I would recommend ceramic coating vs. wrapping. With wrapping, oil or debris can collect on the cloth and potentially cause a fire.
 
I sent my '97 OEM headers to Swain. I can't recall exactly what it cost, but it was less than $400 and I think that included return shipping. Your longer headers w/cats would naturally cost more to coat and ship; but how much more, I don't know. Talk to Swain. Just FYI, their "white lightening" coating has a finish like sandpaper, and likely be harder to clean than coatings which have a smooth finish.

http://swaintech.com/race-coatings/race-coating-descriptions/white-lightning-exhaust-coatings/
 
My gut feel is that your 4yr old after market cats are the culprit. If I was in your shoes, i'd buy a used set of OEM cats instead of spending money on coatings or wrapping which might just be a bandaid. There seems to be some for sale in the marketplace here. While getting the cats up to operating temp is a common issue and is the default reason many smog shops use... most aftermarket cats are simply not as good as OEM or very high quality high flow cats like HJS.

With that said, I ceramic coated my Comptech headers inside and out. The place that did the work is Embee here in SoCal. I've driven this car at the track in all sorts of weather and with a supercharger. I've given them a beating and the coating is still in EXCELLENT shape with good thermal protection. The other place is called Swaintech in the east coast. I would recommend ceramic coating vs. wrapping. With wrapping, oil or debris can collect on the cloth and potentially cause a fire.

i tried used OEM cats - not much luck. i think i have a few sets of them now! i am on my #2 set of aftermarket new cats. my impulse is to put another set of new aftermarket cats on. funny the shop is not suggesting that.
the fire risk concerns me a lot. the 1400 dollar quote for the ceramic i hope includes installation etc. if not, maybe they are $$$ me.
 
i tried used OEM cats - not much luck. i think i have a few sets of them now! i am on my #2 set of aftermarket new cats. my impulse is to put another set of new aftermarket cats on. funny the shop is not suggesting that.
the fire risk concerns me a lot. the 1400 dollar quote for the ceramic i hope includes installation etc. if not, maybe they are $$$ me.
If OEM cats are not working you might have a fundamental problem somewhere else?
 
If OEM cats are not working you might have a fundamental problem somewhere else?

the thing is new cats worked in the past to get the vehicle smogged, and at the last smog check 2 years ago they told me i would probably need new cats next time. so here we are, 2 years later, same shop (different tech)
and they are suggesting wrapping the headers. i have a feeling wrapping the headers is not going to work, then i will need new cats anyway. the cats that are on there are aftermarket, carb approved, but aftermarket cats
have a rep for lasting about one or at best two smog checks. i think i will find some new cats - just the cost of owning this vehicle in Ca . i certainly am not going to enjoy driving my car if i think it might catch fire. it gets hot here in the Summer.
 
I sent my '97 OEM headers to Swain. I can't recall exactly what it cost, but it was less than $400 and I think that included return shipping. Your longer headers w/cats would naturally cost more to coat and ship; but how much more, I don't know. Talk to Swain. Just FYI, their "white lightening" coating has a finish like sandpaper, and likely be harder to clean than coatings which have a smooth finish.

http://swaintech.com/race-coatings/race-coating-descriptions/white-lightning-exhaust-coatings/


hello, I was thinking of doing the white lighting coating by swain. On your installation, did your exhaust note changed? Did it give you a better deeper exhaust note?

Thanks

Frankie
 
I'll never know, Frankie. Installation is still a ways off, and at that point, I'll also be installing new hi-flow cats and new CT exhaust; so any difference in sound the coating might make won't be readily apparent, due to the other changes.
 
Frankie, you can review my build thread (link below) for my additional comments on the coating, but in general... you'd think they would make more of a sound difference but they don't. It's not nearly as extreme of a sound difference as going Test Pipe vs. HF Cats vs. OEM cats for example. The change between long tube headers vs. stock iron early manifolds is more noticeable. Since you're already on the 97+ NA2 manifolds the difference between coating those will be even less apparent. I would argue that coating stock OEM manifolds yields very little bang for your buck. The stock manifolds are pretty thick steel and also has OEM heat shielding which is very good. Any additional heat insulation has diminishing returns IMHO.
 
OK here is what shop told me. one of the cats is only making it to 300 degrees. the cats do not work at 300 degrees. they heated the cat up to 350 and the NOX fell to normal;.
so that is why they think wrapping the headers is the answer.
i am thinking i may just replace the comptech headers with stock manifold. i am so tired of this stuff.
 
I am definitely not an expert on catalyst chemistry and know zip about the California emissions testing regimen; but, I know that in order for the 3 way catalyst to work effectively, the fuel mixture has to be oscillating slightly above and below 14.7. It would be useful to confirm that your pre cat AFRs are operating in that tight range around 14.7. This requires measuring the voltage on O2 sensor with a high impedance measuring device. An oscilloscope would be the ideal tool as you should be able to see the sensor voltage moving up and down slightly during operation. This will require fabricating a jumper or interposing cable to get access to the O2 sensor output. This measurement should only be done after the engine has warmed up and gone into closed loop operation. That also might be good to confirm that the engine is in closed loop operation when the emission tests are being carried out. Unfortunately I don't have access to my service manual and can't remember all the conditions for closed loop operation.

If your AFRs during the testing are not staying close to 14.7 then you might want to consider the condition of your O2 sensors as a possible problem. In the absence of bad AFR numbers, I am not advocating preemptive replacement of the O2 sensors.

Your mechanic is correct that the catalyst needs to be hot for it to work. That is why on the later model NSXs, there is an air pump which briefly injects air into the exhaust manifold during start up. The free O2 in the injected air reacts with the exhaust gas to complete burning of CO causing the catalyst to heat up faster. The catalyst needs the excess O2 associated with periods of lean operation to react with the CO which releases heat which then allows the catalyst to work better on the NOx stuff. That is why the fuel mix needs to oscillate back an forth a little bit around 14.7. Its part of the process of keeping the catalyst happy.

If your AFRs are right around 14.7 and moving up and down slightly, then everything is probably good with your O2 sensors and the FI system. I can't offer any advice as to whether wrapping your headers would make the difference in terms of getting your catalyst up to operating temperature (other than being an absolute pain to do the wrapping). I also have no idea as to whether coating the headers would make a sufficient difference in the exhaust temperature hitting the cats. What might be easier is for the purpose of emissions testing, put a thermal insulator around your converter. This may help the converter reach and sustain its operating temperature for testing purposes. Its definitely a hail Mary tactic. If you try it, don't leave the insulator in place. Under the right operating conditions, you could get the catalyst hot enough to melt its core.

Finally, you have not specified which phase of the NOx test is being failed. Make sure your EGR is working correctly as EGR is a big part of NOx control. There are a number of posts on Prime discussing EGR operation and compliance with he NOx standard.

Something to ask your shop guys, how did they get the catalyst up to 350 degrees and how did they confirm that the car met the standard with that temp? My marginal understanding of catalysts is that the actual catalyst operating temp is way above that (unless they are quoting deg C - which would still be low). Are they talking about the temperature on the external surface of the converter?
 
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Not putting too much brain power into this... The inconsistency of bank 1 vs. bank 2 is interesting. If one bank runs cooler than normal (I don't know what's the optimal "normal" temp by the way) I think this is an issue. It could be ignition timing, or cam timing (have you had a Timing Belt job done or slipped a tooth gear?) or perhaps injectors are clogged and it's running lean and not burning properly.

- - - Updated - - -

I also agree with [MENTION=26435]Old Guy[/MENTION]. 300 degress is way too low. I would have to assume normal temps will be north of 500F. If your timing is way retard then combustion can theoritically combust in the headers and temps will get even higher. FI cars run much hotter depending on timing too

- - - Updated - - -

I think your smog guy is suspect. His feedback is a little bit weird. He's likely taking a temp reading at the heatshields. Don't know...
 
i spoke with shop today, both cats are too cool. i think the sensors are good - they were replaced a few thousand miles ago. it is a shame the fellow who was there 2 years ago left - he seemed really good.
the following was what they told me 2 years ago just before the NSX passed.

//DIAGNOSTICS FOR FAILED EMISSIONS.
VEHICLE FAILLING NOX EMISSIONS:
15MPH 1454
25MPH 1077
ENGINE IN GOOD RUNNING CONDITION. FOUND
AFTERMARKERT O2 SENSORS SWITCHING AT B1
95MS BANK 2 90S, BORDERLINE PASS.
INSPECTED TOPS OF PISTONS WITH SCOPE,
FOUND EXCESSIVE CARBON BUILDUP RECOMMEND
TO PERFORM TOP ENGINE DECARBONIZATION.
AFTER DECARB NOX REDUCTION OF 500 PPM ON
15 & 25. RECOMMEND TO REPLACE
AFTERMARKET O2 SENSOR WITH PAIRED OE
SENSORS. AFTER O2 SENSOR REPLACEMENT
200PPM REDUCTION IN NOX, 25PPM OVFER
STANDARD. CUSTOMER INFORMED THAT THE
TIRES EQUIPPED ARE TALLER THAN STOCK
SIZE, RECOMMENDED TO INSTALL OE TIRES
AND RETEST. AFTER TIRE INSTALLMENT NOX
REDUCED TO 653, 130 POINT BELOW
STANDARD. SMOG TEST PASSED.

There is a copy/paste of everything we did. Hopefully the max allowances aren’t lowered any more that they have. Next step is to get a new set of catalytic converters installed.//
 
Why not simply take your car out for a quick rip on the highway first? It doesn't need to be illegal speeds. Just cruise around in 3rd gear should provide enough high rpm heat.

Then before your test, high idle (2,000rpm) your car to boil the cats for another 5-10 minutes and then you have ample heat in them.

Of course if they are damaged/worn out, this isn't going to work. But if it's heat related, this is the quickest method to ensure you can change the readings without wrappings or coatings. I did this before in my province when emissions testing was required.

The other issue is perhaps the placement of the O2. The rear bank header from Top Speed that I am using is designed incorrectly. The 02 needs to be moved further downstream.
 
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